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    <title>Document</title>
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<body>
    <script>
        // 1.用户输入
        let num=+prompt('请输入分数')
         // 2.判断等级
         num=(100-num)/100
         if(num<=0||num>=100){
        alert('输入错误')
       }else
       if(num<=0.03){
        alert('一级甲等')
       }else if(num<=0.08){
        alert('一级乙等')
       }else if(num<=0.13){
        alert('二级甲等')
       }else if(num<=0.2){
        alert('二级乙等')
       }else if(num<=0.3){
        alert('三级甲等')
       }else if(num<=0.4){
        alert('三级乙等')
       }
        
       
    </script>
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